Aluminum base alloy



United States Patent Ofiice 3,475,166 Patented Oct. 28, 1969 3,475,166ALUMINUM BASE ALLOY Joseph Rafiin, Temple City, Calif., assignor toElectronic Specialty Co. No Drawing. Continuation-impart of applicationsSer. No. 497,557, Oct. 18, 1965, and Ser. No. 561,747, June 30, 1966.This application Jan. 15, 1969, Ser. No.

Int. Cl. C22c 21/02; C221? N04 US. Cl. 75141 14 Claims ABSTRACT OF THEDISCLOSURE This application is a continuation-in-part of applicationSer. No. 497,557, filed Oct. 18, 1965 and now abandoned and of copendingapplication Ser. No. 561,747, filed June 30, 1966, now abandoned.

This invention relates to aluminum alloys, and, more particularly tohigh strength aluminum casting alloys and methods for producing them.

Aluminum alloy castings with high physical strength have long beenneeded, not only to replace more expensive high strength aluminum partsmade by forging, extruding, cold rolling, and machining, but to handlemore intricate design requirements. Aluminum casting alloys for castingparts are available but the strength of such parts has been well belowthat obtainable with machined plates and billets, machined forgings, andwrought assemblies.

At the present time, aluminum casting alloy number 356 is widely used,but it does not have sufficient strength for many design requirements.Aluminum alloys 195 and 357 are also used, but they likewise fall shortof the tensile and yield strengths required for many high strengthaluminum parts. A few special purpose aluminum casting alloys such asTens 50, APM and NA222 and experimental alloys such as ST60 and M710have been used to get relatively high strengths. APM, for example, has anominal composition of about 4%5% copper, about .3% magnesium, andtraces of titanium, silicon, and iron and can be processed to givetensile strength around 45,000 p.s.i., yield strength of around 30,000p.s.i. and elongation of 5% to The copper in the aluminum casting alloyadds to the alloy strength, but

it increases the susceptibility of the alloy to stress corrosion.

This invention provides an improved aluminum base alloy which isvirtually free of stress corrosion problems, and from Which castings canbe made with ultimate tensile strength in excess of 70,000 p.s.i., yieldstrength in excess of 60,000 p.s.i., and about 4% to 10% or moreelongation. Moreover, properties as high as 65,000 p.s.i. tensilestrength, 55,000 p.s.i. yield strength and 8% elongation can beguaranteed in commercial castings with chills, and 60,000 p.s.i.tensile, 50,000 p.s.i. yield and 3% elongation can be obtainedconsistently on sand castings without chills. Such properties arecomparable to those normally achieved only with aluminum forgings ratherthan aluminum castings. The alloy forming the core of this application,therefore, has surpassed all competitors in providing a satisfactoryhigh strength aluminum casting alloy.

Not only are the properties of the present aluminum alloy better thanany others available but the properties of the castings in accordancewith an exemplary embodimerit of this invention remain high at elevatedtemperatures. For example, at 500 F. test results show over 33,000p.s.i. ultimate tensile strength, over 32,000 p.s.i. yield strength and14% elongation. Even at 600 F., the castings have shown over 19,000p.s.i. tensile, over 19,- 000 p.s.i yield and about 16% elongation. Thisis to be contrasted with most aluminum casting alloys which losevirtually all of their strength at such elevated temperatures.

Briefly, the alloy of this invention contains, in addition to itsaluminum base, essentially from about 3.5% to about 6.0% copper, andfrom about .05% to about 3.0% silver and up to about 1% manganese. Foroptimum results, the copper is present in the amount of from about 4.7%and about 5.3% and the silver is present in the amount of from about.40% to about 1.0% and the alloy includes from about .15 to about .40%magneslum.

The percentages referred to throughout the specification and claims arepercentages by weight. The term up to as used herein means from 0% up tothe des- -ignated percentage.

If the copper content varies below 3.5%, the strength of the alloy isdetrimentally effected. With low manganese the preferred lower limit forcopper is about 4.2%. Optimum properties have been obtained with from4.7 to 5.3% copper.

The silver apparently improves the dispersion of copper throughout thealloy to increase its strength and counteracts the tendency of thealuminum alloy to undergo stress corrosion caused by the high percentageof copper. The amount of silver can be increased substantially above 1%without adversely affecting the physical properties of the alloy.However, since silver is an expensive metal, an amount above 1%, or evenabove .7%, unnecessarily adds to the cost of the alloy withoutsignificantly changing its physical properties or its ability to reducestress corrosion.

The tensile strength, yield strength, and elongation are furtherimproved if zinc in the amount of up to 4.0% is added, good resultsbeing achieved with about 1.0% to about 3.0% zinc. Strength is alsoincreased by the addition of a relatively small amount of magnesium inthe range of about .15 to .4%. The best properties have been observedwhen the magnesium content is maintained between .2 and 3% Titanium isbeneficial in assuring fine grain structure in the alloy which isimportant for successful heat solution treatment in accordance with themethod of this invention. The titanium may be present in the amount ofabout .15% to about .7 and preferably is about .20% to about 30%. Insome cases, the titanium is kept at the lower limit, and more is addedwhen the alloy is remelted as this improves the grain structure.

Silicon is kept below .15% in order to avoid burning and iron is keptbelow .15% so that the alloy will properly respond to the heattreatment. For optimum results, both silicon and iron are kept belowabout .1% and preferably below about .05

Boron addition is not essential in making the alloy, but generally asmall amount in the range of .001% to .05% should be added when thealloy is remelted to improve the grain structure.

The manganese content of the alloy may be varied from up to about 1% byweight without detrimentally affecting the alloy. Additions of fromabout .2 to .8% manganese improve the elevated temperature properties ofthe alloy and for that reason are preferred. The best combination ofproperties has been obtained when the manganese content has beenmaintained at about 0.3%.

Elements such as molybdenum and cerium are preferably kept less thanabout 3% each. Chromium is kept below about .5%

The broad and narrow ranges and an exemplary composition of the alloy ofthis invention are given in the following table.

TABLE Percent by weight Broad Narrow Exemplary Elements Range RangeValue Copper 3. 5-6. 0 4. 7-5. 3 4. 9 Silver 05-3. 0 40-1. 0 60 Titanium15-. 7 20-. 30 25 Silicon (maximum). 0-. 15 10 05 Iron (maximum)- 0. 0-.03 Nil Boron 001-. 05 001-. 01 002 Manganese 0-1 8 .3 Molybdenum. 0-. 33 Nil Cerium 0. 3 3 Nil Chromium. 0-. 5 3 Nil Others (each 0. 05 05 NilOthers (tota1). 0. 15 15 Nil Zinc 0-4. 0 1. 0-3. 0 2. 0 Magnesium 0.15-. 4 30 24 luminum Balance Balance Balance A typical melt of the alloywas prepared as follows: about seventy-five pounds of returns (gates andrisers from previous castings to be remelted) is melted down with aboutfifty pounds of high-purity aluminum (99.8% to 99.99% pure aluminum) andabout four pounds of an aluminum-titanium master alloy (5% titanium,balance aluminum) in a silicon carbide crucible in a gas-fired furnace.Temperature control was assured by a chromelalumel thermocouple and apotentiometer. After reaching about 1300 F., 2.75 pounds of electrolyticcopper and .33 pound of silver were added. If zinc were to be included,it would have been added with the copper and silver. After the metalsdissolved, the crucible was filled with an additional forty-five poundsof returns from previous melts to provide a composition within theranges given in the above table. When the temperature reached 1300 F.again, nitrogen was bubbled through the melt with a graphite pipe toremove any deleterious gases, such as hydrogen produced by thedecomposition of moisture, and the temperature was allowed to rise to1400 F. About .50 pound of an aluminum-titanium-boron alloy (5%titanium, 1% boron, and the balance being substantially all aluminum)was added, then about .18 pound of pure magnesium. A check was made tosee if some hydrogen gas was dissolved in the metal, and if the checkwas positive, additional nitrogen was bubbled in until a negative checkwas obtained.

About .10 pound of a grain refiner (a mixture of two parts oftitanium-potassium fluoride with one part of potassium borofluoride) wasthen added to the melt, and after waiting at least ten minutes and whenthe pouring temperature of about 1325 F. to about 1425 F. (depending onthe shape and size of the casting) was reached, the melt was poured intoa mold, including a test bar mold and a sample for chemical analysis. Apouring temperature of 1375 F. is suitable for a wide range of parts.Too low a pouring temperature results in lower mechanical properties.

In a variation of this melting procedure which has also been usedsuccessfully, about one ounce of hexachlorethane pills per 150 pounds ofmetal were plunged into the melt when it reached 1300 F. to removetraces of sodium which may be present. Chlorine gas can be used for thesame purpose. Then the magnesium and the aluminum-titanium-boron alloywere added. After skimming the melt, the grain refiner was added andnitrogen was bubbled through the melt until a check showed that themetal was free of gas. At the same time, the temperature was raised tobetween 1375 F. and 1400 F. The preferred pouring temperatures are thesame irrespective of which of the two melting procedures is used.

A waterless sand casting mold is preferred. Natural bonded sand is alsosuitable, and synthetic sands can be used but they often induce gaspick-up by reaction between the metal and the moisture of the sand.

The cast alloy was then subjected to a solution heat treatment in anelectric, drop quench furnace by heating the casting from three to eighthours at 980 F. to 1000 F. The casting was then quenched in water at atemperature not exceeding 130 F. Quenching sometimes causes warping ofthe cast part, which is straightened in a press or with a plastic orwooden mallet. After straightening the casting as required during thenext three hours, it was age-hardened for eight to twenty hours at 280F. to 340 F.

The purpose of the solution heat treatment is to dissolve thecopper-rich compound deposited around the aluminum-rich matrix duringthe solidification of the alloy without causing the melting of anycompound. The temperature and duration of the solution heat treatment ischosen after consideration of the size, shape, and thickness of thecasting to obtain practically complete dissolution of the eutectic inthe matrix which is checked by micrographic examination.

The purpose of the quenching is to keep the supersaturated solidsolution of the copper rich phase and other intermetallics in thealuminum matrix. Quenching should be as quick and as drastic as possiblewithout producing stress cracks. Quenching with the alloy at 1010 F.made cracks in castings, even in small parts. Quenching with the alloyat 1000 F. did not make cracks in test bars of alloy, but it made somelight surface cracks in a few areas of complex castings. Quenching withthe alloy at 995 F. caused cracks in heavily chilled complex castings,while the same unchilled castings had none. Quenching with the alloy at985 F. did not cause any cracks in castings even up to five feet inlength. Consequently, the alloy of this invention is preferably at 985F., when it is quenched even if solution heat treatment is carried outat 985 F. or 1000 F. In such a case, the temperature is preferablyreduced to about 985 F. prior to quenching. Parts made of the alloy tento fifteen inches long with wall thickness of one-fourth tothree-fourths inch were quenched at 995 F.'without cracking. Thetemperature of the water is preferably no greater than F., and quenchingin water at room temperature appears to improve stress corrosionresistance.

In general, a solution heat-treatment time of about five hours has beensuflicient for parts two and one-half inches thick. A solution heattreatment temperature in the range of 985 to 1000 F. producedsatisfactory results, with optimum results being obtained by reaching995 F. during two to three hours of a five-hour cycle. A typicalsolution heat treatment was one hour at 985 F., followed by three hoursat 995 F., followed by one hour at 985 F. for a total of five hours.

Castings not larger than 15" x 15" and not thicker than A" may besatisfactorily solution heat-treated by heating the parts five hours at995 F. Smaller castings on the order of about 8" x 1" x /2" can be heattreated at 1000 F. for about four hours.

The parts are aged to precipitate the copper compound, with subsequenthardening of the alloy. The temperature and duration of the aging isdetermined by the properties most desired. The tensile strength of thecast alloy generally improves with increased time and temperature up themaximum aging and then begins decreasing as the alloy is overaged.Generally, the ductility of the alloy decreases as the tensile strengthincreases. Increased impact strength is obtained by aging at a lowertemperature for a longer period, e.g., room temperature for at leastfive days, but yield strength is lower. Aging the alloy at 320 F. forabout twenty hours produced very stable material which did not change intime and which also had high resistance to stress corrosion. Aging atthe higher temperature of 340 F. was successfully done in less time, butat the expense of losing a few percentage point in elongation. An alloywith acceptable well-balanced physical properties is obtained by agingat 295 F.

A typical heat treatment for a casting such as a strut for an aircraftlanding gear is as follows: one hour at 985 F., three hours at 995 F.,and one hour at 985 F. for a total of five hours solution heattreatment; quench within five seconds in water at room temperature, andhold the casting twenty-four hours at room temperature; thereafter agetwenty hours at 320 F.

intermetallic compound CuAl This compound has to be dissolved during theheat treatment. Its solubility increases with temperature which probablyaccounts for the fact that this invention uses a temperature range of975 to 1000 F. for heat treatment instead of 940 F. to 970 F. as is usedfor conventional 195 aluminum alloy.

Analysis of another test bar showed the following composition:

Experiments have shown that best properties are obtained when the copperis between about 4.7% and about 5.3%. For example, identicalheat-treated test bars, differing within each set only by coppercontent, had the following tensile properties:

Set No. 1 Set No. 2 Set No. 3 Set N0. 4 Set No. 5

Cu (percent weight) 4. 20 4. 75 4. 75 5. 75 5. 25 5. 75 3. 2 5. 0 5. 06. 0 Ultimate (p.s.i.) 43, 000 58, 000 62, 000 56, 000 61, 000 58,00053, 400 67, 500 59, 700 55, 200 Yield (p.s.i.). 26 000 35, 000 42 00033, 000 44, 000 38, 000 47, 200 60, 600 50, 300 53, 400 Elongation,percent 1 2.0 5. 5 4. 0 8. 0 5. 5 4. 4 1. 2

Best results have been obtained by slowly raising the temperature of thecasting to the solution treating temperature in a series of stages. Thecastings are first heated to a temperature of 940 F. and maintained atthat temperature for a period of eight hours. The temperature of theheat treating furnace is then raised to about 960 F. and againmaintained at that temperature for eight hours. The temperature of thefurnace is then raised another 20 F to 980 F. and the castings aremaintained at this solution heating temperature for another eight hourperiod. The final solution treating temperature is selected on the basisof the alloying content of the. casting, i.e. the amounts of silver,magnesium, manganese, etc., added to the melt. Generally as the alloycontent of the casting increases the final solution heat treatingtemperature should be reduced. The solution treating temperature shouldbe high enough to dissolve the copper-rich phase but must not causemelting of any of the intermetallic compounds. The aging process is bothtime and temperature dependent. If the lower aging temperatures areemployed, the aging times should be increased. For example, it has beenfound that good results are obtained when the castings are aged fortwenty hours at 310 F.

Results of mechanical tests on coupons machined from castings made inaccordance with the above and following currently available high qualitytechniques to promote progressive directional solidification were in thefollowing range: ultimate tensile strength, 59,450 to 70,150 p.s.i.;yield strength (by .2% offset method), 49,500 to 64,450 p.s.i.; andelongation, 5% to 17%.

Chemical compositions of the coupons determined by chemical analysisvaried as follows:

Element: percent by weight Copper 4.74 to 5.55. Magnesium .20 to .31.Titanium .22 to .28. Silver .54 to .61. Manganese Up to .8. Silicon-ironNil. Aluminum Balance.

The alloy of this invention includes a high quantity of copper, part ofwhich contributes to the formation of the Set No. 1

Mg (percent weight) 19 29 38 48 Ultimate (p.s.i 64, 500 70, 600 70, 40030, 000 Yield (p.s.1.) 56, 000 66, 400 67, 400 Elongation, percent- 5. 53. 0 2. 5 5

The .48% magnesium test bar showed some burning. The best range formagnesium is about .20% to 30%, and as indicated by the above example,this range appears to increase the ultimate tensile strength and yieldby about 10%.

Elemental silver is added to the alloy because it increases themechanical strength of the alloy and increases the resistance of thealloy to stress corrosion. The mechanical strength of the alloy isimproved by the addition of as little as 0.2% silver. In the range of.4% to 1.5% silver, the alloy is substantially free of stress corrosion.The mechanical strength appears to be optimum at about 0.5% silver butis little diminished when the silver content is as high as 3.0%. Theeffect of silver on the properties is shown by the following exemplarysets of test bars:

A third set has varying magnesium as well, but still shows that a highpercentage of silver has no detrimental effect on the tensile strength.

Set No. 3

Ag (percent weight) Zinc, when added in amounts between about 1.0% and3.0% also substantially improves the strength as is evidenced by thefollowing exemplary set of test results.

Set No.1

Zn, percent Nil 1.0 2.0 3.0 4.0 Ultimate (p.s.i.) 64,700 68,000 72,20072,700 69,000 Yield (p.s.i.) 56,400 57,800 63,900 64,200 65,200Elongation, percent 5.0 9. 5.0 5.0 2.0

Titanium is a good grain refiner. The range of .20%

to 30% titanium produces a fine grain in the alloy, which facilitatesrequired dispersion of the copper throughout the alloy during solutionheat treatment, with the result that castings can be made which are muchstronger than castings made with previous aluminum casting alloys. Thereseems to be no strength gained by adding more titanium and theelongation drops as the alloy gets richer in titanium. This is shown bythe following set of test bars:

Set No. 1

Ti (percent wei ht) 24 39 54 69 Ultimate (p.s.i 59, 700 59, 400 60, 500200 Yield (p.s.i.) 50, 300 50, 000 51, 000 53, 400 Elongation, percent4. 4 4. 2 4. 2 3. 0

Set No. 2

. 15 15 16 65 59, 700 45, 000 000 50, 300 35, 400 Elongation, percent 2.8. 5 4. 2. 0

To determine the effect of manganese on the strength properties of thealloy, the quantity of manganese was varied up to about 1% and the othercomponents of the alloy were held substantially constant as shown inTable 1.

TABLE 1 Copper, percent 4.11 3. 91 4. 81 3. 55 Iron, percent 04 05 07 04Magnesium, percent- 36 29 27 28 Silicon, percent... .002 015 003 016Zinc, percent- 08 08 10 08 Manganese, percen 28 48 63 94 Titanium,percent 21 23 Boron, percent 023 027 019 028 Aluminum 1 Remainder.

These alloys were cast as chilled plates in said molds and their tensileproperties varied as shown in Table 2.

TABLE 2 The test results shown in all the foregoing examples wereobtained on standard test bars /2 in diameter with 2%" long reducedsection cast in sand mold without chills. The results from each set arenot directly comparable with those of other sets because of difierencesin other variables between sets.

Among other elements that might be added to the alloy, some were verydetrimental, some slightly detrimental, and others had no effect orpossibly light beneficial efiects on the alloy.

Cadmium at .30% caused severe burns and cracks during the heat treatmentwith complete loss of strength and elongation.

Sodium, calcium, and lithium at .02% caused reduction of 10% to 20% ofthe ultimate tensile strength and 30% to 40% reduction of the elongationwith fiaws in the test bars of the alloy.

Cobalt at 30% caused reduction of 20% of the ultimate tensile strengthand 30% reduction of the elongation with coarsening of the grain.

Tin at .005 did not affect the properties of the alloy, but itsassociation with .005 of bismuth caused severe burns and cracks duringthe heat treatment.

Antimony at .005 caused a 10% reduction of ultimate tensile strength anda similar reduction in elongation.

Chromium at .25 and molybdenum at .25 caused a Slight increase ofultimate tensile strength. At .50% molybdenum, there was a slightdecrease of the tensile strength and no significant change for chromiumin this range. Nickel and cerium, each at 30% had no appreciable effecton the propuerties of the alloy. Zirconium at .25% caused a slightdecrease of tensile strength.

I claim:

1. An aluminum base alloy comprising by weight from about 3.5 to about6.0% copper, from about .05 to 3.0% silver, from about .15 to about .4%magnesium, up to about 1% manganese, less than about .05 silicon lessthan .15% iron and the remainder aluminum, said alloy beingcharacterized by yielding sand castings which in the solution treatedand aged condition have yield strengths in excess of 50,000 p.s.i.,ultimate tensile strengths in excess of 60,000 p.s.i., elongations of atleast 5% and high resistance to stress corrosion.

2. An aluminum base alloy as defined in claim 1 wherein said copper isfrom 4.7 to 5.3%, said silver is from .4 to 1% and said magnesium isfrom about .2 to about .3%.

3. A casting produced from the alloy defined in claim 1 and heat treatedto have a yield strength in excess of 50,000 p.s.i., a tensile strengthin excess of 60,000 p.s.i., an elongation of at least 5% and a highresistance to stress corrosion.

4. An aluminum base alloy consisting essentially of from about 3.5 toabout 6.0% copper, from about 0.05 to about 3% silver, from about .15 toabout .4% magnesium as a strengthening agent, up to 1% manganese, lessthan about 0.5% silicon, less than about .05% iron and the balancealuminum.

5. An aluminum base alloy as defined in claim 4 wherein said copper isfrom 4.7 to 5.3%, said silver is from .4 to 1%, said magnesium is from.2 to 3%, and said manganese is from .2 to .8%.

6. A casting produced from the alloy defined in claim 5 said castingbeing heat treated to have a yield strength of at least 50,000 p.s.i., atensile strength of at least 60,000 p.s.i. and an elongation of at least5%.

7. An aluminum base alloy comprising by weight from about 3.5 to about6.0% copper, from about .05 to about 3.0% silver, from about .15 toabout .4% magnesium as a strengthening agent, from about .2 to .8%manganese, from about .15 to .7% titanium as a grain refiner, less thanabout .05% silicon, less than .15% iron and the remainder aluminum, saidalloy being characterized by yielding sand castings which in thesolution treated and aged condition have yield strengths in excess of50,000 p.s.i., ultimate tensile strengths in excess of 60,000 p.s.i.,elongations of at least 5% and a high resistance to stress corrosion.

8. An aluminum base alloy casting in the solution heat treated-agedcondition produced from an aluminum base alloy comprising as essentialelements from about 4.2 to about 6.0% by weight copper, from about .05to about 3.0% by weight silver, up to 1% by weight manganese, less than.1% by weight silicon, less than .15% by weight iron with the balancealuminum, said casting being characterized by having a tensile strengthin excess of 60,000 p.s.i., a yield strength in excess of 50,000 p.s.i.and at least elongation at room temperature and a high tensile strengthand yield strength and a high percentage elongation at elevatedtemperatures.

9. An aluminum base alloy consisting essentially of in percent byweight:

Percent Copper 4.2-6 Silver .41 Magnesium .15-.4 Silicon less than .05Iron less than .10 Manganese 0-1 Others total .15 Aluminum Balance 10. Ahigh strength heat treated casting formed from the alloy of claim 9.

11. An aluminum base alloy comprising in Weight percent:

12. An aluminum base alloy casting in the solution heat treated-agedcondition produced from an aluminum base alloy comprising as essentialelements from about 4.2 to about 6% by weight copper, from about .05 toabout 3% by weight silver, from about .15 to about .4% by Weightmagnesium as a strengthening agent, less than .1% silicon, less than.15% iron with the balance aluminum, said casting being characterized byhaving a tensile strength in excess of 60,000 p.s.i., a yield strengthin excess of 50,000 p.s.i. and at least 5% elongation.

13. An aluminum base base alloy comprising by weight from about 3.5 toabout 6.0% copper, from about .05 to 3% silver, from about .15 to about.4% magnesium, up to about 1% manganese, up to about 4% zinc, less thanabout .05% silicon, less than .15% iron and the remainder aluminum.

14. A casting produced from the alloy defined in claim 13, said castingbeing heat treated to have a yield strength of at least 50,000 p.s.i.and a tensile strength of at least 60,000 p.s.i.

References Cited UNITED STATES PATENTS 1,099,561 6/1914 McAdams 1451,860,947 5/1932 Pacz 75-139 2,240,940 5/1941 Nock 75-141 2,381,2198/1945 Baron 75139 2,459,492 1/ 1949 Bradbury 14832.5 3,414,406 12/1968Doyle et al 75-141 X FOREIGN PATENTS 309,586 3/1930 Great Britain.650,905 3/ 1951 Great Britain.

CHARLES N. LOVELL, Primary Examiner U.S. Cl. X.R.

@52 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,475,166 Dated October 28, 1969 Inventor(s) Joseph Raffin It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Col. 5 line 5 after "up" insert to- Col. 7 line 57 "said" should be-sand-; Col. 8 line 22, "propuerties should be --properties-- Col. 8line 28, "less than about .05 silicon" should be -less than about .051,silicon,--; Col. line 481, "less than about 0.570 silicon should be lessthan about .0570 silicon-- L-.9 SEALED FEB 1 7 1970 ml.) Attem M.Fletcher, Ir,

WILL o g o ne ti Of I E SW m Commissioner 0! Patents

